A variety of techniques and instruments have been developed for use in the removal or repair of tissue in arteries and similar body passageways. A frequent objective of such techniques and instruments is the removal of atherosclerotic plaque in a patient's arteries. Atherosclerosis is characterized by the buildup of fatty deposits (atheromas) in the intimal layer (i.e., under the endothelium) of a patient's blood vessels. Very often over time what initially is deposited as relatively soft, cholesterol-rich atheromatous material hardens into a calcified atherosclerotic plaque. Such atheromas restrict the flow of blood, and therefore often are referred to as stenotic lesions or stenoses, the blocking material being referred to as stenotic material. If left untreated, such stenoses can cause angina, hypertension, myocardial infarction, strokes and the like.
Several kinds of atherectomy devices have been developed for attempting to remove some or all of such stenotic material. In one type of device, such as that shown in U.S. Pat. No. 4,990,134 (Auth), a rotating burr covered with an abrasive cutting material, such as diamond grit (diamond particles or dust), is carried at the distal end of a flexible, rotatable drive shaft.
U.S. Pat. No. 5,314,438 (Shturman) shows another atherectomy device having a rotatable drive shaft with a section of the drive shaft having an enlarged diameter, at least a segment of this enlarged diameter section being covered with an abrasive material to define an abrasive segment of the drive shaft. When rotated at high speeds, the abrasive segment is capable of removing stenotic tissue from an artery.
U.S. Pat. No. 5,314,407 (Auth) shows details of a type of handle which may be used in conjunction with rotational atherectomy devices of the type shown in the Auth '134 and Shturman '438 patents. A handle of the type shown in the Auth '407 patent has been commercialized by Heart Technology, Inc. (Redmond, Wash.), now owned by Boston Scientific Corporation (Natick, Mass.) in the rotational atherectomy device sold under the trademark Rotablator.RTM..
The Rotablator.RTM. device is depicted in FIG. 1, and includes a compressed gas driven turbine located inside a handle housing A. The compressed gas driven turbine is connected to a drive shaft B having an abrasive coated burr C at its distal end. The drive shaft and the burr are rotated at high speeds, typically in the range of, e.g., about 150,000 to about 190,000 rpms. The drive shaft is designed to be advanced over and rotated around a guide wire D. For most of its length the drive shaft is disposed inside a catheter E. The guide wire D must be clamped in some fashion to prevent it from rotating when the turbine and drive shaft are rotated, because uncontrolled rotation of the very flexible distal end portion of the guide wire could cause damage to the artery. For that purpose the Rotablator.RTM. device includes a pneumatic guide wire clamp built into the proximal end portion of the handle housing A. Compressed gas is supplied to the pneumatic guide wire clamp by a flexible gas supply tube F. This gas supply tube F is connected to a rigid conduit G (shown in FIGS. 3-5) that extends through the handle housing A and is connected to a flexible U-shaped tube H which supplies compressed gas to the turbine.
Under certain circumstances, however, it is desirable to override the guide wire clamp and release the guide wire from the clamp even when the turbine and the drive shaft are rotated. For example, it is useful to do so when both the drive shaft and the catheter are advanced over the guide wire to a position within a human artery or when they are removed from the human body. Sometimes it is also useful to override the guide wire clamp to permit advancement or retraction of the guide wire within the rotating drive shaft.
The proximal end portion of the handle of the Rotablator.RTM. device is shown in FIG. 2, and the details of the pneumatic guide wire clamp are shown in FIGS. 3-5. The clamp includes a pair of clamping blocks I on opposite sides of the guide wire. Each clamping block has an inner surface for engaging the guide wire D. Each clamping block also has an outer, tapered surface. A movable pneumatic piston L is provided within the handle, the piston having a proximal end with a central tapered portion in alignment with the outer tapered surfaces of the clamping blocks I.
A coil spring M is provided to normally bias the piston L distally away from the clamping blocks I, thus releasing the guide wire D from the clamp. FIG. 3 shows the clamp in this released position. When compressed gas is provided to a piston chamber N on the distal side of the piston L, the compressed gas urges the piston L proximally, overcoming the force of the spring M and moving the piston into the position shown in FIG. 4. (In FIGS. 4-5 the path of the compressed gas is shown by arrows.) As can be seen in FIG. 4, the tapered proximal end of the piston L presses against the complementary tapered surfaces of the clamping blocks I, resulting in a compression force exerted by the clamping blocks I against the guide wire D. Thus, when compressed gas is supplied to the piston chamber N, the clamping blocks I clamp the guide wire D to prevent rotation or longitudinal movement of the guide wire D. When the supply of compressed gas to the Rotablator.RTM. atherectomy device is interrupted and, as a result, the gas pressure is released from the piston chamber N, the spring M returns the piston L to its distal position (FIG. 3), releasing pressure on the clamping blocks I and the guide wire D.
The Rotablator.RTM. device is constructed so that the piston chamber N is connected pneumatically to the compressed gas tube F that powers both the pneumatic guide wire clamp and the rotatable turbine. The compressed gas supply tube F is connected on one side of the handle housing A to the conduit G positioned inside the handle housing. The conduit G conducts the compressed gas across the handle housing into the flexible U-shaped tube H which supplies the compressed gas to the turbine. Fittings P are used to connect the gas supply tube F and the U-shaped tube H to the conduit G. The conduit G in the handle housing is pneumatically connected to internal passageways which conduct the compressed gas to the piston chamber N. Thus, whenever compressed gas is provided through gas supply tube F to rotate the turbine (and, therefore, the drive shaft of the atherectomy device), the compressed gas is also provided to the piston chamber N to clamp the guide wire D.
An override mechanism is provided to permit the user to release the guide wire clamp even when the compressed gas is supplied to the Rotablator.RTM. atherectomy device and the drive shaft is rotating. This override mechanism consists of a movable spool-type valve R which can be moved from the position shown in FIGS. 3-4 to the position shown in FIG. 5 by pressing on the override button S. In the position shown in FIG. 5, one end of the spool valve R has been moved to a position where it interrupts the supply of compressed gas pressure to the piston chamber N. In this position the spool valve R also vents the piston chamber N to the surrounding atmosphere, releasing the pressure on the piston L and allowing the spring M to return the piston L to its distal position, releasing the clamp even though compressed gas is supplied to rotate the turbine. The spool valve R is biased by a valve spring T to return to the position shown in FIGS. 3-4 when manual pressure on the override button S is released.
The Rotablator.RTM. device's drive shaft begins to rotate very quickly when compressed gas is supplied to the turbine. Because its guide wire clamp can be activated only by supplying compressed gas to the turbine, the drive shaft may begin rotating, and may cause the guide wire D to begin to rotate, before the clamp has been fully activated (i.e., before the force of the spring M has been overcome and the piston L has been moved a sufficient distance to engage the clamping blocks I tightly against the guide wire D to prevent it from rotating). Thus, the Rotablator.RTM. clamp is not always as fast in its action as would be desirable. Moreover, the Rotablator.RTM. device does not provide a brake to prevent the rotation of the turbine and drive shaft when the guide wire clamp is released.